1. Field of the Invention
The present invention relates to a blood purification system, and more particularly to a system in which blood is purified with a filter and which is effectively usable as an artificial kidney system.
2. Description of the Prior Art
Blood purification systems for hemofiltration are used typically as artificial kidney systems. Generally when artificial kidney systems are used for therapy, the filter discharges a filtrate (hereinafter referred to as "total filtrate") which is discarded. The portion of the total filtrate corresponding to the body weight loss can be discarded merely as the "removal filtrate", but when the excess of the filtrate other than the removal filtrate is discarded, the purified blood must be given a substitution fluid in an amount equal to the amount of the excess to maintain the water balance of the patient.
It is known that most optimally the living body should be given the replenishment continuously at the same rate as the discharge of the excess filtrate. To meet these requirements, therefore, it is critical for the artificial kidney system to measure the amounts of the total filtrate, removal filtrate, excess filtrate and substitution fluid.
To supply the substitution fluid continuously in balance with the excess filtrate, systems have been proposed which include those of the volume control type as disclosed typically in Published Unexamined Japanese Patent Application No. 154196/1979 and those of the weight control type a typical example of which is disclosed in U.S. Pat. No. 4,204,957. The former disclosed system is an improvement over the prior art in which the desired amounts were measured only under the control of the speed of rotation of a metering pump and comprises an electromagnetic flow meter for affording measurements with improved accuracy. However, since the system still employs a metering pump for measuring the amount of the removal ultrafiltrate as in the prior art, the system has the serious drawback that the overall accuracy of the system as an artificial kidney system is dependent on the precision of the metering pump and therefore is not higher than is achieved by other conventional systems. The latter system is of the weight measuring type which involves the necessity of storing the whole amount of the ultrafiltrate and using two balances. Accordingly the system has the drawbacks of being large-sized in its entirety, requiring a large space for installation, including a complex-measuring mechanism which must be set in place with care (e.g. to assure the horizontal position of the mechanism) and having greatly reduced portability.
The present invention aims to overcome the foregoing drawbacks and provides an artificial kidney system which can accurately measure the amounts of filtrates and substitution fluid, is compact, inexpensive and convenient from the viewpoint of sanitation.